---------------------------------------------------------- AeroElectric-List Digest Archive --- Total Messages Posted Wed 05/22/19: 6 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 03:47 AM - Re: 2 alternators and 3 questions (Alec Myers) 2. 04:03 AM - Re: 2 alternators and 3 questions (C&K) 3. 04:58 AM - Re: 2 alternators and 3 questions (Art Zemon) 4. 05:45 AM - Re: 2 alternators and 3 questions (user9253) 5. 06:07 AM - Re: 2 alternators and 3 questions (user9253) 6. 08:20 AM - Re: 2 alternators and 3 questions (Robert L. Nuckolls, III) ________________________________ Message 1 _____________________________________ Time: 03:47:14 AM PST US From: Alec Myers Subject: Re: AeroElectric-List: 2 alternators and 3 questions Why not just switch off the pitot heat then? It seems like a huge amount of extra engineering, and the cockpit actions ar e no simpler because according to your comment you still have to decide abou t whether your are using worst case electrical loads or not. On May 22, 2019, at 02:12, Pat Little wrote: NOTE - the above scenario assumes worst-case electrical loads. If the pitot h eat is not being used then it would be simpler to just turn on Stby alt and n ot use the e-bus alt feed. ________________________________ Message 2 _____________________________________ Time: 04:03:54 AM PST US Subject: Re: AeroElectric-List: 2 alternators and 3 questions From: C&K That would be reasonable. I've turned mine on exactly once in 13 years in snow at night and it wasn't needed even then as I pay far more attention to how the controls feel as well as power and attitude. I've done circuits with the airspeed covered up to prove this to myself. It's comforting to have it available when ice is forming but it still can't be completely trusted and it's more important to exit the icing. It would definitely not be used after one of my alternators quit. Ken On 22/05/2019 6:46 AM, Alec Myers wrote: > Why not just switch off the pitot heat then? > It seems like a huge amount of extra engineering, and the cockpit > actions are no simpler because according to your comment you still > have to decide about whether your are using worst case electrical > loads or not. > > > On May 22, 2019, at 02:12, Pat Little > wrote: > > NOTE - the above scenario assumes worst-case electrical loads. If the > pitot heat is not being used then it would be simpler to just turn on > Stby alt and not use the e-bus alt feed. > > ________________________________ Message 3 _____________________________________ Time: 04:58:00 AM PST US From: Art Zemon Subject: Re: AeroElectric-List: 2 alternators and 3 questions Pat, I encourage you to reexamine your load analysis. Here are three points from your Main Bus section: - Flaps motor - 4 amps. The flaps motor rarely operates. This current can be supplied by the battery if the alternator does not have sufficien t capacity. - Stater contactor - 4 amps. Once the engine is running, the starter contactor disengages and draws no current. - Strobe Lights - 4.5 amps. Like you, I have AeroLEDs Pulsar NSP lights on my wing tips and the pair draws 2.40 amps continuous, not 4.50. It looks like I just saved you 10.1 amps. =F0=9F=99=82 As a point of comparison is the load analysis for my airplane. It is in the right column of this drawing. overview.pdf As for your cockpit procedures, they seem like they will certainly work but it is way more effort than I would want to oblige myself to. I fly with both alternator on 100% of the time. If the primary fails, the backup automatically steps in. No pilot action required. If the load is too high for the standby alternator, I will see a low voltage alert and can shed some load. The only two things that I anticipate needing to turn off would be pitot heat (which is almost certainly off anyway) and autopilot servos. Just my opinion, of course: Since we are designing our own airplanes, we have the ability to reduce pilot workload as much as possible. Doing so is a Really Good Idea. -- Art Z. On Wed, May 22, 2019 at 1:30 AM Pat Little wrote: > Bob (and Art and Joe), > Many thanks for your feedback. I realize from your replies that I didn't > explain why I am proposing an e-bus which is normally for reducing batter y > loads, but since my Stby alternator has a strict current limit I think th e > e-bus has a role to play in my system. Here is how I think my design woul d > work, which I hope will make it clear why I am adding the electrical > complexity of the e-bus to achieve a reduction in pilot workload: > > 1) cruise flight, main alternator ON and stby alt OFF - ammeter shows > current from main alternator (our EMS only has a single ammeter gauge) > 2) main alternator fails - LV warning alerts the pilot, he sees current i s > zero and deduces main alternator has failed (or maybe the breaker has > popped which makes it easier to see what has happened) > 3) battery carries the loads for a short while > 4) pilot turns the e-bus alternate feed ON, and the master OFF - this > reduces the electrical loads below the 17A limit of the stby alternator > 5) pilot turns Stby Alt ON. The EMS now shows current from Stby Alt (the > Stby Alt switch is a 3PDT that swaps the ammeter shunt signals as well as > controlling the relay) and pilot can verify loads <17A > 6) continue flight to destination > > In this sequence the benefit of the e-bus is that it gives the pilot a fe w > simple actions to perform in order to ensure the Stby alternator is happy , > and the process doesn't require a lot of heads-down work. > > NOTE - the above scenario assumes worst-case electrical loads. If the > pitot heat is not being used then it would be simpler to just turn on Stb y > alt and not use the e-bus alt feed. > > So, how to choose a system architecture to achieve this? > > Given that I am proposing to use the Stby alt with the master OFF (e-bus > alternate feed ON) I need the output of the Stby alt to feed into the > system upstream of the battery contactor, and that is what Z-13 shows, > whereas Z-12 has it going in downstream where it won't work for my propos ed > design. That is why I want to base my design on Z-13. However, Z-12 shows > the B&C regulator, which is what I have for my main alternator, so i woul d > be incorporating some elements from Z-12 into my drawing. > > I have a loads analysis (I based it on one of the examples from your site > Bob) and I'm attaching it. It is still somewhat incomplete but I'd welcom e > you thoughts. > > Cheers, > Pat > > > On Sun, May 19, 2019 at 8:05 AM Robert L. Nuckolls, III < > nuckolls.bob@aeroelectric.com> wrote: > >> >> Recommend you consider a Z-12 style installation. Leave >> the 17A alternator OFF unless needed during anticipated >> icing conditions . . . another condition that should >> be vanishingly rare -OR- failure of the SD-20. >> You're not going to experience dual alternator failure >> on ANY mission . . . energy rationing with >> an E-bus adds no value. >> >> >> Have you conducted an electrical load analysis >> by flight condition? There are forms that >> assist in organizing the data available >> at https://tinyurl.com/9rt6ymn >> >> Included are some exemplar spread sheets >> uploaded by various List members over >> the years. I did notice that one of >> the .xls spread sheets shows exterior >> lighting as a running load coincident >> with pitot heat. >> >> My instructors taught that exterior >> lights be turned off while in clouds. The >> combination of variable reflection off passing >> clouds combined with flashing of the >> strobe is distracting and can induce >> vertigo . . . I've experienced it >> first hand. >> >> Your RUNNING loads do not include >> landing lights (unless you have a wig-wag >> system or other recognition assist), >> trims, landing gear or flap motors, >> transmitter draws, etc. Just the steady >> state running loads are used to evaluate >> alternator adequacy and in some cases, >> battery supported E-bus operations. >> >> It may be that a well sorted >> load analysis will mitigate concerns >> for alternator adequacy. It also >> helps you define what switches should >> be ON and which ones OFF in the various >> flight conditions. I suspect that your >> suite of alternators will be shown >> to be entirely adequate to all anticipated >> missions . . . especially if your >> exterior lights are all LED. >> >> 20 years ago the most energy hungry >> system on the airplane was position >> lights . . . 2A per bulb x 3 bulbs x >> duration of flight. Xenon flash >> strobes are way up there too. No longer the >> case. >> >> In your case, it seems likely that >> a Z12 architecture with the PM alternator >> as "standby" is possible . . . crunching >> the numbers will confirm/deny that >> assumption. >> >> >> Bob . . . >> > -- https://CheerfulCurmudgeon.com/ *Pray as if everything depends on God. Act as if everything depends on you. * ________________________________ Message 4 _____________________________________ Time: 05:45:51 AM PST US Subject: AeroElectric-List: Re: 2 alternators and 3 questions From: "user9253" An E-Bus is vulnerable to pilot error. What if the pilot inadvertently shuts off the master switch before turning on the E-Bus switch? Now he has to wait for the avionics to reboot. Instead of an E-Bus, how about locating not-so-important switches on the right side and important switches on the left side. Switches could also be color coded. When it is necessary to conserve electrical power, shut off switches on the right side. This can be accomplished with one motion of the hand if the switches are mounted close together. If the pilot later wants to turn on one of the unimportant loads, no problem, just flick on that one load. There is no need to remember which loads are on which bus and no need to juggle master and E-Bus switches. Keep it simple. -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=489340#489340 ________________________________ Message 5 _____________________________________ Time: 06:07:08 AM PST US Subject: AeroElectric-List: Re: 2 alternators and 3 questions From: "user9253" The radio only uses 0.3A, not 2.5 amps. Do NOT count intermittent loads. If the main alternator fails, shut off the landing lights during cruise and save 1.5 amps. The trim motor and relay deck are intermittent loads. Subtract another 1.8 amps. Eliminate the E-Bus diode and save 1/2 amp of wasted power (heat). -------- Joe Gores Read this topic online here: http://forums.matronics.com/viewtopic.php?p=489341#489341 ________________________________ Message 6 _____________________________________ Time: 08:20:23 AM PST US From: "Robert L. Nuckolls, III" Subject: Re: AeroElectric-List: 2 alternators and 3 questions At 01:12 AM 5/22/2019, you wrote: >Bob (and Art and Joe), >Many thanks for your feedback. I realize from your replies that I >didn't explain why I am proposing an e-bus which is normally for >reducing battery loads, but since my Stby alternator has a strict >current limit I think the e-bus has a role to play in my system. >Here is how I think my design would work, which I hope will make it >clear why I am adding the electrical complexity of the e-bus to >achieve a reduction in pilot workload: Show show. I'm packing up to run to Wichita . . . be back tomorrow p.m. I'll let you guys thrash the data/options . . . Bob . . . ------------------------------------------------------------------------------------- Other Matronics Email List Services ------------------------------------------------------------------------------------- Post A New Message aeroelectric-list@matronics.com UN/SUBSCRIBE http://www.matronics.com/subscription List FAQ http://www.matronics.com/FAQ/AeroElectric-List.htm Web Forum Interface To Lists http://forums.matronics.com Matronics List Wiki http://wiki.matronics.com Full Archive Search Engine http://www.matronics.com/search 7-Day List Browse http://www.matronics.com/browse/aeroelectric-list Browse Digests http://www.matronics.com/digest/aeroelectric-list Browse Other Lists http://www.matronics.com/browse Live Online Chat! http://www.matronics.com/chat Archive Downloading http://www.matronics.com/archives Photo Share http://www.matronics.com/photoshare Other Email Lists http://www.matronics.com/emaillists Contributions http://www.matronics.com/contribution ------------------------------------------------------------------------------------- These Email List Services are sponsored solely by Matronics and through the generous Contributions of its members.